It doesn't do any more than that, not multiple displays, and although it will do a 5K display, it doesn't do it well. However for the one thing they claimed it could do, it works as advertised.
Also the FOV is such that there's no point in having a huge screen, since I'd have to move my head from left to right to see everything.
Not sure why the huge screen is relevant. I definitely sometimes prefer to have what amounts to a large display further away, rather than a small display up close. I don't see why you'd make it bigger than your FOV.
Note that these numbers are half the actual pixel count in each dimension because MacOS defaults to assuming the display is a 2x Retina Display.
So, if you choose the 1920x1080 option you get what I see using my actual 4K display. It also avoids the downsampling, because the stream itself is 4K and so is sharper.
I don't know why Apple set the default for 5K downsampled.
My XReal Air glasses are okay for mirroring a single 1080p display, but becomes fatiguing on the eyes.
I've seen people complain about fatigue after 5 hours on a plane, so it's not impossible but it sounds like it's better than most.
I bought them as “nreal” in dec 2022, I don’t know they updated the hardware when they rebranded.